The percentile parameter may be less then zero, i.e.,
percentile = -20 equals percentile = 80

size : scalar or tuple, optional

See footprint, below

footprint : array, optional

Either size or footprint must be defined. size gives
the shape that is taken from the input array, at every element
position, to define the input to the filter function.
footprint is a boolean array that specifies (implicitly) a
shape, but also which of the elements within this shape will get
passed to the filter function. Thus size=(n,m) is equivalent
to footprint=np.ones((n,m)). We adjust size to the number
of dimensions of the input array, so that, if the input array is
shape (10,10,10), and size is 2, then the actual size used is
(2,2,2).

output : array, optional

The output parameter passes an array in which to store the
filter output.

mode : {‘reflect’,’constant’,’nearest’,’mirror’, ‘wrap’}, optional

The mode parameter determines how the array borders are
handled, where cval is the value when mode is equal to
‘constant’. Default is ‘reflect’

cval : scalar, optional

Value to fill past edges of input if mode is ‘constant’. Default
is 0.0

origin : scalar, optional

The ``origin`` parameter controls the placement of the filter. Default 0 :